Cargo handling systems, such as those used by aircraft for transport of heavy containerized cargo or pallets, (also referred to as unit load devices (ULDs)) typically include roller trays containing transport rollers which rollably support the cargo, and a power drive unit (PDU) for facilitating loading and unloading operations.
Conventionally, braking function may be provided in the PDU and/or by adding braking rollers to the trays. To achieve braking function in the PDU, solenoid brakes may be utilized. However, solenoid brakes are typically biased to engage or alternatively disengage in a power-off state, with typical systems being designed to lose braking function in the power-off state.
Accordingly, such cargo handling systems typically utilize additional braking rollers to provide braking force in the power-off state. Therefore, in typical lower deck applications, which may contain between about 48 to 64 PDUs, the number of braking rollers may equal about 70% of the number of PDUs. Such braking rollers may react with a braking force in one or both directions, and may impose undesired resistance in normal operation. Additionally, such braking rollers take up space that may otherwise be utilized for transport rollers or restraint devices in the system.